1. Field of the Invention
The present invention relates to a method for treating plastics, which enables producing processed plastics that can be readily reduced in size. It also relates to a method for treating plastics, which is capable of converting plastics, including chlorine-containing plastics such as poly(vinyl chloride), into plastics substantially free from chlorine. It further relates to a solid fuel and a reducing agent for ores obtained from the same method for treating plastics.
2. State of the Art
Recently, a method of producing solid fuel from waste plastics has been developed as a solution for overcoming the problem of effectively using waste plastics. This method is based on the fact that the flammability of plastics drastically increases when it is finely pulverized, and that it becomes a useful fuel resource.
The technology of converting plastics into a solid fuel comprises, as is reported in, for instance, Plastics, Vol.47, No. 7, page 60, directly size-reducing plastics by using a grinding machine.
However, the method described above suffers problems. For instance, in the case of hard plastics, their size reduction not only is limited to a granularity of about 1 to 2 mm, but also consumes much time and cost. In the case of fibrous and film plastics, grinding thereof is difficult, and hence, they require complicated process steps including melting and solidifying them separately before subjecting them to grinding. Moreover, in these cases, it is also necessary to remove insoluble matters such as glasses and metals before grinding.
Moreover, plastics containing chlorine, such as poly(vinyl chloride), generates a harmful substance, i.e., hydrogen chloride, when combusted. When subjecting these plastics to a heat treatment, they must be treated separately from other plastics because they generate gaseous hydrogen chloride which causes corrosion of vessels and piping. Thus, they require a separate heat treatment and the like to remove hydrogen chloride therefrom.
In the light of the aforementioned circumstances, a method of treating plastics using a solvent has been proposed.
More specifically, JP-B-Sho.57-16160 and JP-B-Sho.52-38594 (the term "JP-B-" referred herein signifies "an examined published Japanese patent application") disclose a method of treating plastics in petroleum or mineral oils.
However, the solids obtained by the method disclosed in the references above are in a swelled state, and are difficult to grind into fine particles. Moreover, the solid products thus obtained have been found to be apt to agglomerate during grinding or after grinding, and are likely to cause clogging of piping during their transportation from the site of grinding to the site of burning.
Thus, currently known methods have failed to provide a fine powder of solid fuel having excellent combustibility that can be easily handled.
Furthermore, a method of regenerating poly(vinyl chloride) which comprises dissolving waste poly(vinyl chloride) into a solvent and removing the solvent thereafter is disclosed in International Patent Publication No. W 094/06854. Because the object of this method is to regenerate poly(vinyl chloride), the treatment is performed at low temperatures so that dehydrochlorination does not occur, and that the structure of poly(vinyl chloride) is retained.
Accordingly, the regenerated material produced according to W 094/06854 is not suitable for use as a solid fuel, because, for instance, it contains chlorine, and does not grind well due to the low temperature treatment.
Also known is a technique for mixing waste plastics with a solvent and subjecting the resulting mixture to a decomposition reaction so as to finally obtain the plastics in the form of liquid fuel or gas (reference is made to JP-B-Sho.52-22672, JP-A-Hei.7-207279, and JP-A-Hei.8-81685, where, the term "JP-A-" as referred herein signifies "an unexamined published Japanese patent application"). However, this method is not a technique for producing solid fuel.